Research On Key Technologies Of Chaotic Multitone Covert Communication System

Due to the broadcast characteristics of wireless communication and the development of electronic countermeasure technology,how to realize signal waveform concealment and information hiding through coding,modulation and transmission waveform design in the physical layer has become an important issue to be solved in the field of wireless communication security.As a special communication mode with concealment as the main goal,wireless covert communication is an information hiding method based on wireless communication.It has important application prospect in military communication in complex confrontation environment and intelligence communication in physical isolation environment.At present,the main technologies used in covert communication systems are replacing redundant frame fields,introducing additional coding domain errors,inserting additional signal bands,and introducing additional signal noise.However,these technologies are still difficult to balance the performance of low probability of detection(LPD)and anti-noncooperative demodulation.The main purpose of the paper is to explore a covert communication system with LPD and anti-non-cooperative demodulation characteristics by analyzing the current theory of constant rate covert communication based on uncertainty,integrating chaotic communication technology and transform domain communication system(TDCS)technology,which is different from the present multiple access coding and modulation technology.The specific research idea is to explore a multitone communication method to achieve waveform concealment and propose a method for transmitting baseband information by chaotic multitone group(MTG)and mathematical algorithm according to TDCS and chaos theory.Then,the chaos encryption method is introduced into multitone modulation to improve the anti-decipherability ability of this new coding modulation technology.Finally,in order to reduce the detection probability of the signal,the time-varying parameter is introduced to increase the detection uncertainty of the non-cooperative reciever.Meanwhile,to improve the frequency band utilization and integrate with the current communication system,the scheme of time-varying chaotic multitone overlapping covert communication system is proposed based on orthogonal frequency division multiplexing(OFDM).These technologies are flexible and compatible with the hardware architecture of existing communication systems,and can be used to develop new covert communication systems for satellites,aircraft,ground,submarines and ships.The main contents of this paper are as follows:(1)According to the analysis of chaotic frequency hopping,TDCS and overlapping covert communication technology,the design of constraint conditions parameter to realize LPD of non-cooperative parties are studied with the cover of legitimate communication links in the overlapping covert communication model.Based on steganography theory,the design requirements of TDCS covert communication signals,the defects of current baseband modulation and coding methods in anti-recognition are analyzed.It is concluded that a new coding and modulation method needs to be studied to achieve low probability of recognition(LPR)covert communication.(2)To solve the coding scheme of signal waveform concealment and the problem of antinon-cooperative party recognition,a multitone communication method based on chaos theory is proposed.The generation of multitone set,MTG coding and the design method of discrete chaotic index sequence are studied,and the preliminary scheme of information modulation using MTG intermediate frequency point first moment mapping algorithm is given.Then,the detection and demodulation methods of multitone signals are studied.To validate the performance of communication methods,the reliability of the communication method is theoretically analyzed and the simulation system is constructed.Therefore,the bit error rate(BER)performance and the distribution characteristics of multitone points are analyzed.Besides,the anti-recognition performance of the communication method is verified based on the singular spectrum entropy method.(3)To further improve the anti-deciphering ability of chaotic multitone communication method and realize anti-non-cooperative demodulation,an anti-deciphering multitone modulation method based on chaotic cryptography is proposed to suppress the obvious statistical characteristics of different types of MTG caused by the first-order moment mathematical mapping algorithm.Firstly,the MTG is pre-coded and iteratively calculated as one of the parameters of spatiotemporal chaotic system.The iterative results are symbolized according to the baseband data type,thus completing the multi-to-one mapping between MTG codebook and baseband data.Then the chaotic scrambling idea is used to design the index sequence,so that the receiver cannot analyze the detected MTG and the corresponding frequency information by statistical methods.Theoretical analysis and experimental data show that the method can not only resist conventional statistical attacks,but also can achieve anti-brute force and select plaintext attacks with the the number of MTG and the key space,thus ensuring the security of the modulation level.(4)Aiming at the problem of reducing the non-cooperative detection probability and improving the spectrum utilization,a scheme of chaotic multitone overlapping covert communication based on timing information is proposed,which uses OFDM to study the corresponding modulation and demodulation technology.The timing information is introduced as a parameter to control the number of MTG monophonies to increase the randomness of the signal.The covert communication technology that can be embedded in the current fifth generation(5G)communication system is realized.Theoretical analysis and experimental simulation results show that the system can ensure the original reliability andreduce the detection probability with the uncertainty to the eavesdropper detection,which has stronger anti-interference ability than conventional covert communication methods.It provides a good solution to avoid hidden signal source exposure or reduce the detection probability of non-cooperative nodes in overlapping covert communication model.